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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

For a second consecutive year the globe experienced its hottest year on record, beating the 2014 record by more than 0.1℃. From May 2015 onwards, each month set a temperature record for that particular month, a pattern that has yet to end.

In all three global temperature series, 2015 stands out as the hottest year.UK Met Office, Author provided

The record-breaking temperature anomaly in 2015 (around 1℃ higher, on average, than what would be expected in a world without humans) was in large part due to human-caused climate change. A small fraction of the heat was because of a major El Niño event, which developed midway through 2015 and ran into this year.

During El Niño events we see warmer sea surface temperatures in the central and eastern Pacific Ocean. A resulting transfer of heat from the ocean into the lower atmosphere causes a temporary warming effect. In La Niña seasons, the opposite happens.

Extreme events around the world…

At regional scales we also saw many extreme events last year. The downward trend in Arctic sea ice continued, with the lowest annual maximum extent on record. Alaska’s winter was almost non-existent, with many Arctic mammals and fish being forced to change their behaviour and shift their habitats.

Many extreme heatwaves occurred in 2015. These included a deadly hot spell in India and Pakistan and severe heat events in Europe and North America. Combined, these events killed thousands of people.

Seasonal-scale extreme heat occurred over many parts of the globe. There were many more warm days and nights than normal over much of Europe in summer, and in Russia and North America in spring.

Extreme events occurred around the world in 2015.NOAA NCEI

Across the world there were more tropical cyclones than normal, mainly due to increased cyclone activity across the Pacific basin, and many significant flood events. On the other hand, large areas suffered severe drought (14% of the land surface, up from 8% in 2014).

…including in Australia

In Australia, probably the most significant climate extreme we had was the record heat in October.

The country experienced its biggest monthly temperature anomaly on record – almost 3℃ above the historical national average. The frequency of very warm days was also well above average. This unusual early heat triggered bushfires across the southeast.

Even given the El Niño event (which normally warms up Australia in spring and summer), the maximum temperature records that were set were, for example, at least six times more likely in Melbourne than they would have been in the absence of human-caused climate change.

Australia experienced its hottest October on record in 2015.Bureau of Meteorology, Author provided

For 2015 as a whole, Australia experienced its fifth-warmest year on record. Nine out of 12 months were warmer than average.

A continuation of climate change trends

Besides the record heat, the world saw many other unwanted records tumble in 2015, providing ever more extensive evidence for the effect that humans are having on the climate. Greenhouse gas concentrations (the primary cause of our changing climate) rose to record high levels, with carbon dioxide concentrations passing the 400 parts per million mark at many sites. The year’s margin of increase in atmospheric carbon dioxide concentrations was also the largest on record.

Unfortunately, in many ways, the climate of 2015 is not likely to stand out as especially unusual in a few years’ time. More record hot years are likely, with associated extreme weather events, as greenhouse gas concentrations continue to climb.

Only with rapid and substantial cuts to these emissions will it be possible to limit global warming to well below 2℃, a key aim of the Paris climate agreement, and reduce the likelihood of yet more climate records tumbling.

Comments

'Unfortunately, in many ways, the climate of 2015 is not likely to stand out as especially unusual in a few years’ time. More record hot years are likely, with associated extreme weather events, as greenhouse gas concentrations continue to climb.'

I hear 'skeptics' claiming that we are going to soon be entering a cooling phase that is likely to be of long duration due to lower sun activity and changes in ocean cycles. My expectation (based on my limited knowledge, I'm not a scientist and I appologise for any scientific illiteracy in my writing ), was that if this is the case we would not see a downward trend in surface temperatures, due to the warming effect of CO2, but we would go back to the slower rise in temperatures we had for a number of years prior to the beginning of the current El Nino. But you seem to have a clear expectation of further record temperatures in the coming years. Is this because you are not expecting the negative natural cycles or you think that the effects of CO2 are so potent they will significantly counter the natural cycles?

I'm also wondering in general what natural cycles are expected between now and 2050, and what the resulting patterns might be. I'd also be interested to know if any skeptic has stuck his or her neck out and made some firm predictions for the next 5, 10, 20 years, such as a clear downward trend in surface temperature, recovering arctic sea ice, a downward trend in sea level etc. Thanks.

" I hear 'skeptics' claiming that we are going to soon be entering a cooling phase that is likely to be of long duration due to lower sun activity and changes in ocean cycles."

I'm no expert, just an interested observer of the climate change debate, however I have repeatedly read articles in responsible publications like this saying the effect of solar cycles on temperatures is simply not that large, and not enough to hugely alter the increasing greenhouse affect and IPCC projections of warming going forward.

I also read an article saying that the oceans are basically entering a warming phase according to scientists, that could last several decades at least as below.

This is the PDO (the pacific decadal oscillation) and its been in a cool phase for some years and may have been a factor in the pause since 1998 (slight slow down). The signs are its now entering a warm phase that could be decades long, and will simply add to warming from greenhouse gases, and could counteract any change in solar irradiance . It's certainly a cyclical event so has to change sooner or later. So the sceptics seem to have it 100% wrong and around the wrong way.

Australia seems to have had a particularly cold winter that looks to have coincided with not the bottom of the current solar cycle but we are getting toward the bottom of it! It would be interesting to see if next years winter is even colder.

Saying that there are several factors making the Northern Hemisphere warmer than the Southern Hemisphere. This means the Arctic gets the lions share of Global Warming and if the Arctic sea ice melts the ocean currents will change meaning in ways that are unpredictable and so the earths distribution of heat will change in ways that are unpredictable.

You would have to guess a lot of people will freeze as there is no longer impetus for the heat from the equator to move toward the pole that has no ice...

Thanks for the replies. I read the post article, which looks like we will experience warming from the PDO but then I read that we are entering a cooling period in the AMO. https://theconversation.com/the-atlantic-is-entering-a-cool-phase-that-will-change-the-worlds-weather-42497. Whether these two effects will balance each other out regarding overall surface tempeature, I haven't a clue.

Good article in your link. The PDO is swinging positive to a warming phase, and the AMO could be swinging to a cooling phase, all over the next decade or so. Remember neither of these drives global warming from greenhouse gases, and can only influence that trend to some extent.

However the Pacific ocean is larger, so would be the dominant force globally and is entering a warming phase. We are heading for warming globally as a whole, but some north atlantic coastal areas could maybe cool or warm more slowly, or have associated dry periods.